A conflict that occurs during synchronization can be resolved differently by different synchronization partners in a peer-to-peer synchronization environment. One such peer-to-peer synchronization environment and its underlying hardware/software interface system is disclosed in detail in the Foundational Patent Applications recited earlier herein. In summary, the Foundational Patent Applications describe a hardware/software interface system (such as, but not limited to, an operating system) where, among other things, autonomous units of storable information (Items) comprise several component change units (CUs) that constitute the basic data change element for synchronization. Each CU has associated metadata that enables the synchronization system to track what changes need to be updated on peer computer systems as well as what changes received from other peer computer systems should be applied.
One exemplary form of basic synchronization for systems using change units and metadata for synchronization (or similar structures) can be generally described in terms of a single change unit for an item that exists on two peer computer systems. In regard to this single change unit, a first peer, Partner A (or, more simply, “A”), requests changes from a second peer, Partner B (or, more simply, “B”), by transmitting to B its current metadata (Ma) pertaining to its replica of the change unit (CUa). Partner B, upon receiving Ma (corresponding to CUa), compares this metadata with its own metadata (Mb) for its replica of the same change unit (CUb). Then, if Mb reflects any changes to CUb that are not reflected in Ma, B transmits both CUb and Mb to A; otherwise B only transmits its Mb to A (or, alternately, transmits a “no updates” indicator to A) since CUa already reflects all updates made to CUb and thus copying CUb from B to A is unnecessary.
Based on B's response to its sync request, if A receives only Mb back from B (or, alternately, a “no update” indicator) but no CUb then A knows that CUa is either the same as or more updated than CUb. However, if A receives both Mb and CUb back from B, then A must then determine, by a comparison of Ma to Mb, whether CUb is more updated than CUa or whether CUa and CUb have conflicting changes. If CUb is more updated than CUa, A then updates CUa with CUb and A also updates Ma with Mb. On the other hand, if CUa and CUb have conflicting changes, then A resolves that conflict according to its local conflict resolution procedures. For example, if A's conflict resolution procedure in this case is to choose a local solution over a remote solution, the A would continue to retain CUa (rejecting CUb's changes) and update Ma to include all updates already reflection Ma and Mb (the union of Ma and Mb). Thereafter, when B then syncs with A using the same procedure (and presuming no intervening additional changes), it will conclude that CUa is more updated that CUb and update CUb with CUa.
This basic change-unit-and-metadata (CUAM) approach to synchronization is simple and effective for a two-peer synchronization community. However, with three or more peers, this simple approach can result in divergence of the data such that two systems may reach different conflict resolution solutions but have identical metadata, and thus the logical inconsistency cannot be recognized nor adequately corrected in the peer community. A detailed example of this phenomenon is provided later herein.
In order to force the data on all peers to converge, what is needed in the art is a synchronization methodology for synchronization systems of various types to correctly identify and propagate specific conflict resolutions between the peers in a synchronization community and arbitrate between differing resolutions for the same conflict in order to ensure the consistent convergence onto a single resolution of the conflict across all relevant peers.